This invention relates to ion sources, and particularly to the type of ion source in which a compound of the material of a desired ion is dissociated in a plasma discharge process to provide a beam of charged particles. The beam includes the desired ions, which are generally subsequently separated from the beam by mass-charge separation techniques. While not so limited, the invention has particular utility in the production of singly charged boron ions for use in ion implantation apparatus.
One problem with prior art plasma dissociation ion sources is that it has not been known how to control fully the dissociation process, whereby the proportion of the desired ion in the output current is generally significantly less than what, at least, would appear to be possible. For example, if singly charged boron ions are desired from a source gas of a compound of boron, the total quantity of boron in the desired ionic form has, heretofore, been significantly less than the total quantity of boron present in the gas. That is, because it has not been known how to control fully the extent and completeness of the dissociation process, most of the boron present in the gas remains tied-up in non-useful molecular and electrically neutral forms.
Thus, for the purpose of increasing the usefulness and efficiency of such ion sources, a need exists for controlling the dissociation process for selecting and optimizing the proportions of selected ions in the ion source output current.